Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $235.92   13.528%   $267.8353   $267.84   $267.85   $267.80  
  Purchase #2 $227.44   3.293%   $234.9296   $234.93   $234.95   $234.90  
  Purchase #3 $195.85   9.386%   $214.2325   $214.23   $214.25   $214.20  
  Purchase #4 $121.81   3.456%   $126.0198   $126.02   $126.00   $126.00  
  Purchase #5 $224.76   12.484%   $252.819   $252.82   $252.80   $252.80  
  Purchase #6 $220.64   4.202%   $229.9113   $229.91   $229.90   $229.90  
  Purchase #7 $226.86   12.223%   $254.5891   $254.59   $254.60   $254.60  
  7 purchase totals = $1,453.28       $1,580.3366   $1,580.34   $1,580.35   $1,580.20